This invention relates generally to endoluminal devices, such as stents, grafts, and/or prostheses and, more specifically, to the detection of endoleaks or changes in morphology after implantation of a prosthesis.
A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft.
A prosthesis may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, a prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called xe2x80x9cminimally invasive techniquesxe2x80x9d in which the prosthesis, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a deployment system or xe2x80x9cintroducerxe2x80x9d to the site where it is required. The introducer may enter the body through the patient""s skin, or by a xe2x80x9ccut downxe2x80x9d technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the prosthesis deployment location, the introducer is manipulated to cause the prosthesis to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the prosthesis), whereupon the prosthesis expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration. Various types of stent architectures are known in the art, including many designs comprising a filament or number of filaments, such as a wire or wires, wound or braided into a particular configuration.
One common application for the implantation of prostheses is for treatment of abdominal aortic aneurysms (AAA). AAA stents are typically placed into the aorta and iliac bifurcation with a covering to isolate the aneurysm from the blood. After the aneurysm has been isolated for some time, endoleaks may occur due to worn fabric or other reasons. Because the isolated aneurysm has become weak as a result of being isolated, once the leak starts, blood flow and pressure is slowly restored to the aneurysm, and the aneurysm may rupture. Currently, leaks are detected during follow-up angiograms and MRIs, but if the follow up visit does not coincide with the duration of time within which the leak must be treated, the undetected endoleak may result in a ruptured aneurysm that is fatal to the patient. Another method of detecting an endoleak is checking the aortic pressure with respect to the aneurysm sac pressure. This can be accomplished by introducing a pressure-sensing needle into the aneurysm sac through the skin while checking the aortic pressure using an invasive procedure.
In addition to endoleaks, other problems may also ensue after implantation of a prosthesis that can cause problems if undetected. For example, after the aneurysm is isolated, the morphology of the prosthesis may change as the aneurysm shrinks. The changing morphology may lead to iliac occlusions that occur with little to no forewarning. Current non-invasive monitoring techniques are not always successful in detecting such changing morphology.
Thus, there is a need in the art to provide non-invasive means of detecting endoleaks and/or the changing morphology of implanted prostheses.
The invention comprises an endoluminal device comprising a prosthesis having at least one indicator member affixed to the prosthesis, such as woven into or attached to the stent or graft or sandwiched therebetween, that is adapted to be remotely monitored to indicate a change in pressure or morphology of the prosthesis. The indicator member may comprise an optical fiber, a strain gauge, or a first material having a first magnetic resonance imaging (MRI) susceptibility value that contrasts with a second MRI susceptibility value of a second material that comprises one or more remaining members of the prosthesis.
The invention also comprises a prosthesis monitoring system, and a subassembly therefor, comprising a prosthesis for implantation in a lumen, the prosthesis comprising at least a first optical fiber member having a first end affixed to the prosthesis and a second end. The system further comprises means for sending an input optical signal through the optical fiber and receiving an output optical signal, such means attached to the first optical fiber second end. A transmitter may be used to transfer the information related to the return signal to a remote receiver. Where the prosthesis is deployed to isolate an aneurysm having an aneurysm sac, the system may further comprise a second optical fiber having a first end deployed in the aneurysm sac and a second end connected to the means sending signals. The means for sending/receiving signals and the transmitter may be subcutaneously implanted, thus forming an implantable subassembly. The subassembly may further comprise a subcutaneously implantable battery for supplying power to the system and a remotely-activatable, subcutaneously implantable switch for turning power on and off to the system from the battery. The subassembly may cooperate with external electronics for displaying the data externally. The first optical fiber may be configured to measure bending of the optical fiber, or the first, and optionally the second, optical fiber may be configured to measure pressure at the first end of the optical fiber.
The invention further comprises a prosthesis monitoring system at least partially implantable within a body for detecting a change in morphology of an implanted prosthesis. The morphology change detection system comprises an indicator affixed to the prosthesis and adapted to indicate the change in morphology in a remotely measurable manner, and remote monitoring means for detecting the indication of the change in morphology indicated by the indicator. In one embodiment, the indicator may comprise at least one member integral to the prosthesis that has a first magnetic resonance imaging (MRI) susceptibility value that contrasts with a second MRI susceptibility value of a second material that comprises one or more remaining members of the prosthesis, the member having a configuration adapted to change in response to the change in morphology. In this embodiment, the remote monitoring means comprises a MRI device adapted to detect the configuration of the member. In other embodiments, the system comprises an implantable optical fiber for conveying information from the indicator to the remote monitoring means.
The invention also comprises a prosthesis monitoring system at least partially implantable within a body for detecting an endoleak in an implanted prosthesis. The endoleak detection system comprises an implantable indicator adapted to indicate a change in pressure attributable to an endoleak and remote monitoring means for detecting the indication of the change in pressure provided by the indicator. The indicator may be affixed to the prosthesis, such as a strain gauge or the indicator may be adapted to be deployed in or on the aneurysm sac. In one embodiment, the indicator comprises a first optical fiber member adapted to be mounted in the aneurysm sac to detect pressure and the system further comprises means for sending at least a first input optical signal and receiving at least a first output optical signal through at least the first optical fiber. In one embodiment, the indicator consists only of the pressure-detecting optical fiber member in the aneurysm sac, but in another embodiment, the indicator comprises at least a second pressure-detecting optical fiber member affixed to the prosthesis. In this embodiment, the signal means is further adapted to send a second input optical signal and receive a second output optical signal through the second optical fiber.
The invention also comprises methods for using the systems described herein. A method for detecting a change in morphology of a prosthesis implanted within a body comprises implanting the prosthesis in a lumen of the body, the prosthesis comprising an indicator affixed thereto and adapted to indicate the change in morphology of the prosthesis. The change in morphology indicated by the indicator is detected by remote monitoring means outside the body. Where the indicator comprises a first MRI-susceptible material that contrasts with a second MRI-susceptible material that comprises one or more remaining members of the prosthesis, the monitoring step comprises first using an MRI device to perform a first MRI procedure and record a result thereof as a baseline morphology. Then, the MRI device is used to perform a subsequent MRI procedure, and a result of the subsequent MRI procedure is compared to the baseline morphology to determine if there has been any change in morphology.
A method for detecting an endoleak in an implanted prosthesis comprises the steps of implanting the prosthesis in a body lumen and implanting a monitoring system comprising an indicator for detecting a change in aneurysm sac pressure, the indicator in communication with means for conveying information from the indicator to a remote monitor outside the body. The method further comprises activating the monitoring system to cause the indicator to communicate with the means for conveying and to cause the means for conveying to transmit information to the remote monitoring means. The method may comprise implanting the prosthesis to isolate an aneurysm that comprises an aneurysm sac, and deploying a first optical fiber in the aneurysm sac.
Where the indicator consists only of the first optical fiber, the method may further comprise periodically monitoring pressure measured using the first optical fiber over a period of time sufficient to establish a baseline profile and then monitoring changes from the baseline profile, interpreting a change from the baseline profile greater than a threshold value as an indication of an endoleak. Where the prosthesis further comprises a second optical fiber integral to the stent and coupled to the monitoring system, the method may further comprise periodically monitoring a differential pressure between the first optical fiber and the second optical fiber and interpreting a change in the differential pressure greater than a threshold pressure as an indication of an endoleak.